The present invention relates to multispeed bicycles having derailleurs and, in particular, to an apparatus for the cancellation and linearization of derailleur spring forces so that the effort necessary to shift such a bicycle is reduced.
Multiple speed bicycle transmissions are well known, providing a bicycle on either or both of its free wheel or chain driven wheel with one or more clusters of progressively sized gears coaxially arranged and a drive chain movable from one gear to another. Because each gear in the cluster is of a different size, the movement of the drive chain from one to another effectively changes the drive ratio of the bicycle. This movement of the drive chain is typically accomplished by a device known as a derailleur, which carries the chain from gear to gear.
The travel of the derailleur is controlled by a cable, the end of which is connected to a shift lever within reach of the rider. The derailleur has spring means which biases the derailleur position to a first end of the gear cluster. When the control cable is pulled by movement of the shift lever, the derailleur position travels away from the first end toward a second opposite end of the gear cluster, causing the load upon the bias spring to be increased, which in turn increases the tension in the shift cable.
As the derailleur is positioned further from the first end of its range of travel, increasingly greater effort must be applied to the shift lever to overcome the increasing load of the derailleur bias spring. This nonlinearity in the shift lever forces is undesirable.
In my copending Ser. No. 679,439, filed Apr. 2, 1991, a motorized electromechanical apparatus is disclosed for facilitating the shifting of the derailleur. The apparatus provides means for the force cancellation of the inherent tension in the shift cable to minimize the size, weight, and power requirements for effecting the gear change. While the apparatus disclosed in my aforementioned application is most satisfactory and highly useful, there are times when a motorized shift apparatus is not desirable and/or is not cost efficient, and a mechanical shift device will need to be used. If so, the problems of overcoming the high force of the derailleur biasing spring function forces and applied tension forces will remain.
It is the prime object of the present invention to provide a derailleur shift apparatus in which force cancellation is mechanically overcome in a simple and cost-efficient manner.
It is another object of the present invention to provide a system for reducing the nonlinearity of shift lever forces necessary to change gears of a multispeed bicycle.
It is also an object of the present invention to provide a device which improves the accuracy and speed with which gears can be mechanically shifted in a multispeed bicycle.
It is another object of the present invention to provide a device which achieves the aforementioned objects while being easily retrofitted to a conventional derailleur equipped multispeed bicycle.
Further objects and advantages of the instant invention will become apparent from the following disclosure.